Field of the Invention
The present invention relates to a sealing device, and more particularly relates to a sealing device in which a screw achieving a fluid pumping action is provided in a sliding portion of a seal lip. The sealing device according to the present invention is used, for example, in an automobile-related field, or used in a field of a general purpose machine.
Description of the Conventional Art
There has been conventionally known a sealing device in which a screw achieving a pumping action applied to a sealed fluid is provided in an atmosphere side lateral face of a seal lip sliding portion for improving a sealing performance in relation to the sealed fluid such as an oil. In the case that the other sliding member (hereinafter, refer simply to a shaft) such as a rotary shaft rotates in both forward and reverse directions, a bidirectional screw 53 is provided in an atmosphere side lateral face 52 of a sliding portion of a seal lip 51, as shown in FIG. 5.
The bidirectional screw 53 is structured by circumferentially and alternately lining up and arranging forward direction screws 54 which achieve a sealing function based on a pumping action when the shaft rotates in a forward direction (an arrow C), and reverse direction screws 55 which achieve the sealing function based on the pumping action when the shaft rotates in a reverse direction, one by one, or several by several, or several tens by several tens. Each of the screws 54 and 55 is formed into a so-called parallel screw in which its longitudinally perpendicular cross sectional shape (including a screw height and a screw width) is formed uniformly over a whole length of the screw.
The prior art described above can achieve an excellent sealing performance on the basis of the pumping action of each of the screws 54 and 55, however, since each of the screws 54 and 55 is formed as the parallel screw as mentioned above, there is a problem that the pumping action is lowered in the case that wear caused by the sliding motion makes progress.
In order to countermeasure the problem mentioned above, it can be thought that each of the forward direction screw 54 and the reverse direction screw 55 is formed into a ship bottom-like screw in place of the parallel screw, as shown in FIG. 6 which shows a comparative example with the present invention. Since the ship bottom-like screw is provide with a shape that a screw height is enlarged little by little from a lip leading end 56 toward an atmosphere side B, the screw height thereof is hard to be lowered even if the wear makes progress. Accordingly, the pumping action is hard to be lowered.
However, even in the case that each of the forward direction screw 54 and the reverse direction screw 55 is formed into the ship bottom-like screw as mentioned above, sealed fluid may leak by spray from the screws 54 and 55. In order to suppress the leak by spray from the screws 54 and 55, an additional countermeasure is necessary.